1. Field of Invention
The present invention relates to a driving circuit system for use in an active-matrix-type electro-optical device and for driving the electro-optical device, and also to an electro-optical device driven by this driving circuit system.
2. Description of Related Art
Generally, in an active matrix type electro-optical device, a plurality of scanning lines and a plurality of data lines are arranged in a matrix, and pixel electrodes are formed via switching elements, such as thin film diodes (hereinafter referred to as “TFDs”) and thin film transistors (hereinafter referred to as “TFTs”) in correspondence with the intersections of the matrix.
In the electro-optical device configured as described above, scanning signals are sequentially supplied to the respective scanning lines by a scanning-line driving circuit. More specifically, the scanning-line driving circuit has a Y-direction shift register formed of unit circuits in multiple stages in the Y direction (vertical direction), which is the direction in which the scanning lines are arranged. First, the Y-direction shift register sequentially transfers a start pulse, which is supplied from an external image signal processing circuit at the start of a vertical scanning period, based on the period of a Y-direction clock signal CLY (and its inverted signal CLY′), which is used as the reference of vertical scanning, output from the external image signal processing circuit. The Y-direction shift register then supplies transfer signals as scanning signals from the respective stages of the unit circuits to the corresponding scanning lines.
Meanwhile, the data lines are driven by a data-line driving circuit. That is, the data-line driving circuit is configured to supply sampling control signals to sampling switches, which sample an image signal supplied to an image signal line in correspondence with the individual data lines, in synchronization with the above-described operation of sequentially supplying scanning signals. More specifically, the data-line driving circuit has a multiple-stage X-direction shift register in the X direction (horizontal direction), which is the direction in which the data lines are arranged. First, the X-direction shift register sequentially transfers a start pulse, which is supplied from the external image signal processing circuit at the start of a horizontal scanning period, based on the period of an X-direction clock signal CLX (and its inverted signal CLX′), which is used as the reference of horizontal scanning, output from the image signal processing circuit. The X-direction shift register then outputs transfer signals as sampling control signals from the respective stages of the unit circuits to the sampling switches connected to the corresponding data lines. Subsequently, the sampling switches respectively sample the image signal supplied to the image signal line according to the sampling control signals and supply the sampled image signal to the corresponding data lines.
As discussed above, generally, in the active-matrix-type electro-optical device, vertical scanning based on a field unit or a frame unit, namely, field scanning or frame scanning, is performed in accordance with the scanning signals and sampling control signals sequentially output from the shift registers.
When being put into practical use, this type of electro-optical device often has a built-in driving circuit system in which the aforementioned scanning-line driving circuit and the data-line driving circuit are formed, together with the switching elements connected to the pixel electrodes, on one of a pair of substrates forming the electro-optical device. In this case, a small space occupied by peripheral circuits including the driving circuits makes it possible to miniaturize the entire device. Additionally, active elements, which form the peripheral circuits, are formed by the same process step as the switching elements for driving the pixel electrodes, thereby enhancing the manufacturing efficiency of the whole device and decreasing the cost.
The size of the substrates is a factor that defines the size of the entire electro-optical device. Accordingly, the formation of a large peripheral portion on which the scanning-line driving circuit and the data-line driving circuit are formed in the peripheral region on the substrates, in relation to a screen display portion, contradicts the basic demand in this technical field for miniaturizing the entire electro-optical device and increasing relatively the screen display portion in relation to the size of the electro-optical device.
Thus, for the formation of the driving circuits on the substrate, in the Y-direction shift register of the scanning-line driving circuit, the circuit pitch in the Y direction of each unit circuit (hereinafter simply referred to as the “circuit pitch of the Y-direction shift register”) is adjusted to the same pitch as that of the scanning lines. Accordingly, the Y-direction width of the portion required for forming the scanning-line driving circuit can be set to be substantially equal to the Y-direction width of the screen display portion. Similarly, in the X-direction shift register of the data-line driving circuit, the circuit pitch in the X direction of each unit circuit (hereinafter simply referred to as the “circuit pitch of the X-direction shift register”) and the pitch in the X direction of the sampling switches of the sampling circuit (hereinafter simply referred to as the “pitch of the sampling switch”) are adjusted to be the same pitch as that of the data lines. Accordingly, the X-direction width of the portion required for forming the data-line driving circuit can be set to be substantially equal to the X-direction width of the screen display portion. This makes it possible to reduce the widths in the X direction and in the Y direction of the substrates, thereby preventing a large scale of substrates.
These days, there is an intense demand for a higher level of image quality in the electro-optical device. In order to implement higher-definition images, it is thus necessary to reduce the pixel pitch to a very small size and also to driving a greater number of scanning lines and data lines at a higher frequency.
However, each unit circuit of the above-described shift registers is provided with a plurality of relatively complicated active elements. For example, each unit circuit requires at least three clocked inverters, each formed of four TFTs, positive and negative power sources for each clocked inverter, and wiring patterns for supplying a clock signal and its inverted signal. Accordingly, in the configuration in which peripheral circuits, such as the driving circuits, are formed on the substrate of the electro-optical device, as the pixel pitch is becoming smaller, it is more difficult to adjust the circuit pitches of the above-described Y-direction and X-direction shift registers to the same pitches of the scanning lines and the data lines. For example, under current circumstances, the smallest-possible circuit pitch of the shift registers is, in a practical sense, about 20 μm, which hampers a decrease in the pixel pitch.